.corner{
    width: 200px;
    height: 32px;
    position:fixed;
    right: 20px;
    bottom: 5px;
    background: url("/ai/welcome-dark.png") no-repeat;
    background-size: 100% 100%;
    opacity: .5;
    z-index: -1;
}
.corner-dark{
    width: 200px;
    height: 32px;
    position:fixed;
    right: 20px;
    bottom: 5px;
    background: url("/ai/welcome.png") no-repeat;
    background-size: 100% 100%;
    opacity: .5;
    z-index: -1;
}